Until the early 2000's avalanche photodiodes (APDs) were widely deployed in 10 Gb/s optical receivers. In subsequent years, the use of APDs for high-capacity systems declined as a result of their limited gain-bandwidth, the transition to coherent detection, and the development of high efficiency modulation techniques. Recently, the rapid growth of optical-fiber communications systems that utilize baud rates up to 25 Gbit/s as represented by 100-Gbit/s Ethernet (100 GbE) has led to a resurgence of research on APDs. Two figures of merit for APD optical receivers are the excess noise factor and the gain-bandwidth product. Both are linked to the k factor, which is the ratio of the electron, α, and hole, β, ionization coefficients. The mean-squared shot-noise current can be expressed as the equation:ishot2=2q(Iph+Idark)M2F(M)Δf  (1)where Iph and Idark are the primary photocurrent and dark current, respectively, M is the avalanche gain, Δf is the bandwidth, and F(M) is the excess noise factor. In the local field model the excess noise factor is given by the equation:F(M)=kM+(1−k)(2−1/M).  (2)
The excess noise factor increases with increasing gain but increases more slowly for lower values of k. The present inventors point out that higher receiver sensitivities are achieved with low k values. The gain-bandwidth product is important because it is essential that the APD operate at sufficiently high gain to overcome the noise limitation of the following amplifier at the transmission bit rate. The present inventors point out that the lower the k value, the higher the gain bandwidth product of an APD. Initially, for bit rates ≤10 Gb/s, InP/InGaAs APDs were the photodetectors that achieved the highest receiver sensitivities. However, the relatively high k value of InP, k˜0.5, resulted in high excess noise and gain-bandwidth products of <100 GHz. Recently, AlInAs/InGaAs APDs, for which the k value is ˜0.2; these APDs achieved 235 GHz gain-bandwidth product and receiver sensitivity of −21 dBm at 25 Gb/s and 10−12 bit error rate. However, the “champion” material candidate for high performance APDs is Si. It has demonstrated k values ˜0.02 and gain-bandwidth products >340 GHz. Unfortunately, as the present inventors point out, the bandgap of Si obviates operation at wavelengths >1.0 μm. There have been many efforts in the past 20 years to achieve the low noise and high gain-bandwidth product of Si at telecommunications wavelengths (1.3 μm to 1.6 μm). One approach to utilize the excellent gain characteristics of Si has been to combine a Ge absorption region with a Si multiplication layer in a separate absorption, charge, and multiplication (SACM) APD. In optical receivers, these APDs have achieved sensitivities as high as those of the best III-V compound APDs but not superior, as would have been expected from their low k value. This sensitivity limitation stems from the high dark current, that arises from the lattice mismatch between Ge and Si, which contributes enough to the noise to offset the lower excess noise factor.
In light of the above, a need arises APDs with optimal k values and excellent gain/noise characteristics similar to that of Si with the low dark current and high speed of the III-V compound APDs.
Overview
An aspect of an aspect of an embodiment of the present invention provides, among other things, an avalanche photodiode that may comprise: a first contact layer; a multiplication layer adjacent to the first contact layer, wherein the multiplication layer comprises AlInAsSb; a charge layer adjacent to the multiplication layer opposite the first contact layer, wherein the charge layer comprises AlInAsSb; an absorption layer adjacent to the charge layer, opposite the multiplication layer, wherein the absorption layer comprises AlInAsSb; a blocking layer adjacent to the absorption layer, opposite the charge layer; and second contact layer adjacent the blocking layer, opposite the absorption layer.
An aspect of an aspect of an embodiment of the present invention provides, among other things, an avalanche photodiode, and related method of manufacture and method of use thereof, that includes a first contact layer; a multiplication layer, wherein said multiplication layer comprises AlInAsSb; a charge, wherein said charge layer comprises AlInAsSb; an absorption, wherein said absorption layer comprises AlInAsSb; a blocking layer; and second contact layer.
An aspect of an aspect of an embodiment of the present invention provides, among other things, an avalanche photodiodes (and related method of manufacture and use) with a multiplication region, charge region and an absorption region composed of an aluminum indium arsenide antimonide (AlInAsSb) alloy.
An aspect of an embodiment of the present invention provides, among other things, SACM avalanche photodiodes fabricated from AlxIn1-xAsySb1-y, grown on GaSb. The excess noise factor of the AlxIn1-xAsySb1-y SACM APDs multiplication is characterized by a k value of 0.01 and gain as high as 50 has been achieved. Further, the lattice-matched AlxIn1-xAsySb1-y, absorbing region extends the operating wavelength to the short-wavelength infrared (SWIR) spectrum. These APDs combine the excellent gain/noise characteristics of Si with the low dark current and high speed of the III-V compound APDs.
An aspect of an embodiment of the present invention provides, among other things, an avalanche photodiode, fabricated from AlxIn1-xAsySb1-y, with low excess noise corresponding to k=0.015 and peak quantum efficiency. Furthermore, since AlxIn1-xAsySb1-y has a direct bandgap, it provides higher bandwidths than Si, which is typically limited by transit times. An aspect of an embodiment of the new materials system provides, but not limited thereto, an innovative alternative to Si for detection across the visible and near-infrared wavelengths.
These and other objects, along with advantages and features of various aspects of embodiments of the invention disclosed herein, will be made more apparent from the description, drawings and claims that follow.